A magnetic disk drive used as an information storage device has a magnetic head section having a conversion element read element and/or write element. The write element records and erases data into/from data bits arranged on a circular track of an information recording medium, and the read element reads a magnetic signal recorded by the write element. The magnetic head section is mounted on a slider body section so as to be formed into a head slider. The head slider is connected to a suspension arm. The suspension arm applies a pressing force to the head slider in a direction to the recording medium. When the recording medium is rotated, the head slider flies on an air film formed on the recording medium by rotation of the recording medium.
A surface of the recording medium has a protective layer, which is covered with a lubricating layer, for protecting the magnetic head section from wear and corrosion. When a magnetic space between the magnetic head and the recording medium or flying amount is reduced to improve magnetic recording areal density, the lubricant layer is decreased in thickness to the same level as a monomolecular layer. A monomolecular layer of a lubricant is extremely importantly and is kept at an interface between the head slider and the recording medium in order to keep reliability at the interface between the head slider and the recording medium. Mobility is an key property of the lubricant, as the lubricant should be immobile enough so that it is not easily displaced by slider-disk contacts, but mobile enough that it easily replenishes any placed lubricant.
The head slider has an air-bearing surface facing a recording medium. While the recording medium is rotated, the recording medium drags air under the head slider along the air-bearing surface in a direction approximately parallel to the tangential velocity of the recording medium. As the air passes beneath the air bearing surface, air is compressed to cause a pressure between the disk and the air bearing surface to increase, which creates a hydrodynamics lifting force that counteracts the load force and causes the slider to lift and fly above or in close proximity to the medium surface.
Once the magnetic disk drive is operated, four kinds of forces of hydrodynamic, van der Waals and electrostatic pressures, and air shearing stress, are generated by motion of the bead slider, leading to movement of the lubricating layer. Among the four kinds of force, the air shearing force is the dominant one for movement of a lubricant. The air shearing force moves the lubricant to the bottom of the head slider, and droplets of the lubricant are formed in an interfacial portion between the head and the disk.
In a head slider having an extremely low flying height, it has been found that an extremely strong relationship exists between motion of the lubricant droplets and an air flow on the bottom of the head slider. Most of the lubricant droplets are moved to an outflow end of the head slider by the air shearing force.
To achieve a head slider that operates at a required flying height, a head slider has been designed, which has an air-bearing surface having a special shape on a surface facing a medium. It is now observed that as average flying height of the head slider is continuously decreased, accumulation of the lubricant droplets on the flying surface of the head slider, and contact or falling of a deposited lubricant to/onto the recording medium increasingly cause a read/write error. However, the low-flying head slider has been configured without considering accumulation of the lubricant on a portion near a conversion element section. When the lubricant accumulated on the conversion element section of the head slider contacts to or falls onto the recording medium, the read/write error may be caused as described before. Particularly, if a write error occurs, data may be irreparably lost.
To avoid a phenomenon that a lubricant drawn into a negative pressure groove is accumulated on a stepped portion at an outflow end, and the accumulated lubricant gradually grows into a large droplet, and eventually contacts to or falls onto a surface of a recording medium, Japanese Patent Publication No. 2003-99910 describes a head slider in which an intermediate step is provided between a step bearing surface and a negative pressure groove surface to reduce height of the stepped portion, on which the lubricant may be accumulated, so that accumulated amount is decreased.
Thickness of the lubricant is now decreased to an atom level for a low magnetic spacing between the conversion element section of the head slider and the recording medium in order to increase recording density. Moreover, flying height of the head slider is also reduced in order to reduce the magnetic spacing. The magnetic spacing has been thus reduced, and thereby pressure on the conversion element section has been increased, as a result, droplets of the lubricant are now easily accumulated on the conversion element section due to a backflow from an outflow end of the head slider.
FIGS. 5A and 5B show a flow on an air-bearing surface of a previous head slider. In the head slider, backflows 504 and 505 from an outflow end occur near both side portions of an outflow side rail. Stagnation line 502 and 503 are found, at which a flow to be generated has a velocity of zero in the length direction of the head slider due to the backflows respectively, thereby a flow rate near the center rail having the conversion element section is decreased. Furthermore, the position 502 is connected to the outflow side rail, and the droplets of the lubricant are led to the outflow side rail along such a connection line.
In a recent head slider, a structure is found, in which when the magnetic spacing is reduced, the outflow side rail is provided while avoiding reaching the outflow end of the head slider to prevent contact of the outflow end of the head slider to a recording medium. Particularly, when a heater is provided in a head section to thermally expand a portion near a write/read element section so as to be protruded from a flying surface, the rail is often provided while avoiding reaching the outflow end of the head slider to prevent contact of the flying surface of the expanded rail to the medium.
In this way, when a rail section is provided in a manner of avoiding reaching the outflow end of the head slider, a backflow 506 from the outflow end occurs even at a wake side from the rail section having a write/read element mounted thereon. Droplets of the lubricant, which are led to the outflow side rail by the backflow 506, flow as shown by 507 along the outflow end of the outflow side rail, and then the droplets are accumulated on a corner of the outflow side rail. Today, it is known that when the accumulated droplets fall from the end of the outflow side rail, oscillation occurs in the head slider, leading to an error during recording/reproducing.
To increase recording density without reducing reliability of a magnetic disk drive, flying amount of the head slider needs to be decreased, and control needs to be performed to suppress accumulation of the lubricant droplets on the outflow end of the conversion element section of the head slider due to the backflow from the outflow end of the head slider.